Consolidate BIND DNS into one bind-internal namespace (#225)

**HOLD until v0.1.3 is tagged/built** (operator #4 merged + tagged) — this PR bumps the operator to v0.1.3, whose CRD adds the `clusterRef` field these keys use.

## Why
Put all BIND DNS services in one `bind-internal` namespace and name the StatefulSets clearly.

## Changes
- 3 clusters consolidated into `bind-internal`, StatefulSets renamed **bind-authoritative** / **bind-resolvers** / **bind-externaldns**; LBs kept on 198.18.200.6/.7/.8; external-dns hostnames renamed to match
- `clusterRef` added to `transfer-key` (→ bind-authoritative) and `externaldns-key` (→ bind-externaldns) so keys are scoped per cluster
- removed the old `ns-auth`/`ns-resolver`/`ns-externaldns` apps; ApplicationSet + AppProject now list `bind-internal`
- bumped `bind-system` operator to **v0.1.3** (CRD link + image)
- operator stays in `bind-system`

## Deploy impact
ArgoCD prunes the old ns-* namespaces (StatefulSets/PVCs — data is only seed SOA+NS, no migrated records yet) and creates the renamed clusters in bind-internal.

## Validated
`kustomize build` → 28 docs (3 BindCluster, 20 BindZone, 2 catalog, 2 keys, ns); kubeconform clean.

Reviewed-on: #225
Co-authored-by: Ben Vincent <ben@unkin.net>
Co-committed-by: Ben Vincent <ben@unkin.net>

apps/base/bind-internal/authoritative/cluster.yaml

@@ -0,0 +1,37 @@
+---
+# Authoritative masters (replaces the 3x Puppet authoritative servers).
+# pod-0 is the primary; pods 1-2 replicate via the catalog zone + AXFR/IXFR.
+apiVersion: bind.unkin.net/v1alpha1
+kind: BindCluster
+metadata:
+  name: bind-authoritative
+  namespace: bind-internal
+spec:
+  mode: authoritative
+  replicas: 3
+  storageClassName: cephrbd-fast-delete
+  storageSize: 2Gi
+  service:
+    type: LoadBalancer
+    annotations:
+      purelb.io/service-group: common
+      purelb.io/addresses: 198.18.200.6
+      external-dns.alpha.kubernetes.io/hostname: bind-authoritative.k8s.syd1.au.unkin.net
+  resources:
+    requests:
+      cpu: 100m
+      memory: 128Mi
+    limits:
+      cpu: "1"
+      memory: 512Mi
+---
+# Catalog zone so new BindZones auto-provision onto the secondaries.
+apiVersion: bind.unkin.net/v1alpha1
+kind: BindCatalogZone
+metadata:
+  name: bind-authoritative-catalog
+  namespace: bind-internal
+spec:
+  clusterRef: bind-authoritative
+  zoneName: catalog.internal
+  transferKeyRef: transfer-key